12 December 2007

The Feyerabend Project & Gerry Sussman

Computer Science is in deep trouble. Structured design is a failure. Systems, as currently engineered, are brittle and fragile. They cannot be easily adapted to new situations. Small changes in requirements entail large changes in the structure and configuration. Small errors in the programs that prescribe the behavior of the system can lead to large errors in the desired behavior. Indeed, current computational systems are unreasonably dependent on the correctness of the implementation, and they cannot be easily modified to account for errors in the design, errors in the specifications, or the inevitable evolution of the requirements for which the design was commissioned. (Just imagine what happens if you cut a random wire in your computer!) This problem is structural. This is not a complexity problem. It will not be solved by some form of modularity. We need new ideas. We need a new set of engineering principles that can be applied to effectively build flexible, robust, evolvable, and efficient systems.

In the design of any significant system there are many implementation plans proposed for every component at every level of detail. However, in the system that is finally delivered this diversity of plans is lost and usually only one unified plan is adopted and implemented. As in an ecological system, the loss of diversity in the traditional engineering process has serious consequences for robustness.

This fragility and inflexibility must not be allowed to continue. The systems of the future must be both flexible and reliable. They must be tolerant of bugs and must be adaptable to new conditions. To advance beyond the existing problems we must change, in a fundamental way, the nature of the language we use to describe computational systems. We must develop languages that prescribe the computational system as cooperating combinations of redundant processes.